We have a partner company with the following problem
with "Lock Fairness" (see sample code below)
in the Solaris JVM (all versions from what they tell me).
I tried it in Windows JVM and it does exhibit fairness.
However, it does not in Solaris JVM.

public class TestWeirdness {

     static class SpinThread implements Runnable {
         SpinThread(Object lock) {
             this.lock = lock;
         }

         public void run() {
             System.err.println("SpinThread started");
             int i = 0;
             while (true) {
                 synchronized (lock) {
                     try {
                         Thread.sleep(500); System.err.println("loop " + i++);
                     } catch (InterruptedException e) {
                         e.printStackTrace();
                     }
                 }
             }
         }

         private Object lock;
     }

     public static void main(String[] args) {
         Object lock = new Object();
         SpinThread st = new SpinThread(lock);
         Thread t = new Thread(st);
         t.start();

         try {
             Thread.sleep(1500);
         } catch (InterruptedException e) {
             e.printStackTrace();
         }

         System.err.println("Trying to acquire lock");
         synchronized (lock) {
             System.err.println("Acquired lock");
         }

         System.exit(0);
     }
}

On Windohs (NT 4.0) and RedHat 6.2, I get

    % java TestWeirdness
    SpinThread started
    loop 0
    loop 1
    Trying to acquire lock
    loop 2
    Acquired lock

On Solaris (I've tried 7, 8, 9) I get

    % java TestWeirdness
    SpinThread started
    loop 0
    loop 1
    Trying to acquire lock
    loop 2
    loop 3
    loop 4
    loop 5
    loop 6
    loop 7
    loop 8
    loop 9
    loop 10

and sometimes it eventually acquires the lock after dozens or
hundreds of iterations.